Method of regulating the halogen content of hydrocarbon conversion catalysts

ABSTRACT

Process, and product, for an over-chlorinated hydrocarbon conversion catalyst having a porous support (e.g. alumina) with at least one having metal deposited thereon (e.g. platinum) -where the catalyst is stabilized by the steps of calcination followed by washing with water (preferably distilled) to remove substantially all water soluble chlorides leaving a chlorine content of between 0.5 and 1.2% (calculated as an element) of the weight of the catalyst and drying.

United States Patent 11.91

Engelhard et al.

[ Dec. 3, 1974 METHOD OF REGULATING THE HALOGEN CONTENT OF HYDROCARBON CONVERSION CATALYSTS [75] Inventors: Philippe Engelhard; Joseph Edouard Weisang, both of Le Havre, France [73] Assignee: Compagnie Francaise de Raffinage,

Paris, France [22] Filed: Aug. 23, 1972 21 Appl. No.: 283,062

[30] Foreign Application Priority Data Aug. 26, 1971 France 71.31010 [52] U.S. Cl 252/442, 252/441, 208/139 [51] Int. Cl B0lj 11/78 [58] Field of Search 252/441, 442

[56] References Cited UNITED STATES PATENTS 3,117,076 1/1964 Brennan et a1. 208/139 x Primary Examiner-Patrick P. Garvin Attorney, Agent, or Firm-Curtis, Morris & Safford 5 7 ABSTRACT Process, and product, for an over-chlorinated hydrocarbon conversion catalyst having a porous support (e.g. alumina) with at least one having metal deposited thereon (e.g. platinum) where the catalyst is stabilized by the steps of calcination followed by washing with water (preferably distilled) to remove substantially all water soluble chlorides leaving a chlorine content of between 0.5 and 1.2% (calculated as an element) of the weight of the catalyst and drying.

17 Claims, No Drawings METHOD .OF REGULATING THE HALOGEN CONTENT OF HYDROCARBON CONVERSION CATALYSTS The present invention relates to an improvement in the preparation of hydrocarbon conversion catalysts. More particularly, it relates to a method which makes it possible to regulate the content of halogenated compounds in said catalysts.

It is known that hydrocarbon conversion catalysts are bifunctional. Namely, they have a cracking function on the one hand and a hydrogenatiomdehydrogenation function on the other hand. Such double-function catalysts are generally formed of a porous support of refractory mineral oxide whose acidity confers the cracking function, and of a supported heavy metal of groups V to VIII of the periodic table of elements, in free or combined form, and to which the hydrogenation dehydrogenation properties are attributed. Recent work has shown that these catalysts which can be improved by deposit of several of the elements belonging to the abovementioned groups to which there can be added the heavy elements of group IV, (Ge, Sn, Pb).

Such catalysts, can be used in numerous reactions, such as isomerization, hydrocracking, hydrocyclization and hydroreforming of hydrocarbon charges.

The beneficial effect of the presence ofhalogens on i the catalytic compositions used in the hydrocarbon conversion processes has been noted. This effect makes itself felt on the acid properties of the catalyst. The halogens, particularly chorine and fluorine, and especially chlorine, can be present in various forms: they can be combined with components of the support on the one hand and/or with elements deposited on the support on the other hand. At present very little is known of the chemical nature of these compounds which are formed.

Upon the starting of a reactor, the chlorine content of a hydroreforrning catalyst is generally between 0.1 and 1.5% (calculated as an element) of the weight of the catalyst, and preferably between 0.5 and 1.2%. This content is not constant, and it decreases during the operation of the catalysts; It is necessary to chlorinate the catalyst intermittently during the operation of the reactor, for instance by the admission of gaseous chlorine into the stream of gas.

The halogen present may have been introduced during the preparation of the support. In this way, for instance, one can obtain an aluminum hydroxide gel by the addition of ammonium hydroxide to aluminum chloride, the aluminum hydroxide being then calcined to alumina. The halogen can also be introduced upon subsequent treatment of the support, for instance by contacting of the alumina with circulating hydrochloric acid. Finally, the halogen can be introduced upon the deposit of the hydrogenation-dehydrogenation compounds. One can thus, for instance, deposit platinum by impregnation of the support witha hydrochloric acid solution of hexachloroplatinic acid.

It would appear that the operator is not always the master of the amount of halogen which he deposits during the preparation of the catalyst, or, more precisely, that as this amount is not independent, it is fixed by the values ofother parameters,'such as the method of preparation of the support or the platinumcontent. The applicants have now observed that, all other things being equal. the performance of a conversion catalyst depends only on the halogen content thereof. but does not depend on the conventional processes used to introduce said halogen into the composition of the catalyst. It is thus known, for instance, that the optimum content of elementary chloride in hydroreforming catalysts is between 0.5 and 1.2%, and preferably between 0.5 and 0.9%, of the total weight of the catalyst. It is therefore advantageous to be able to adjust the content of elementary halogen in conversion catalysts.

An object of the present invention is to provide a method of regulating the halogen content of hydrocarbon conversion catalysts.

' For this purpose one can contemplate either a method of regulating the halogen content by the halogenation .of an insufficiently halogenated catalyst, a method of preparing the catalyst which directly produces the optimum halogen content, or else the dehalogenation of an overly halogenated catalyst.

The applicants have shown that dehalogenation is a simple process which produces excellent results.

The dehalogenation of catalysts has already been described in the three following US. Pat. Nos. 3,239,450, 3,523,912 and 3,189,559.

US. Pat. No. 3,239,450 concerns the preparation of a hydrocarbon conversion catalyst in which anactivated support containing alumina or magnesia is contacted with an aqueous solution of a fluoride of a metal having hydrogenating-dehydrogenating properties (preferably'nickel). In one embodiment of the invention, the fluorides which are not chemisorbed on the support are extracted with water.

US. Pat. No. 3,523,912 concerns a method of preparing a hydrocarbon conversion catalyst which consists in the coprecipitation of the components of the catalyst. The catalyst prepared has a low chlorine content (less than 0.25%). This content can be obtained by washing and ion exchange, effected on the wet coprecipitate.

US. Pat. No. 3,189,559 concerns the complete dechlorination of a catalystcontaining platinum or alumina by causing a solution of ammonia to'move over it.

The processes described in these patents do not include the treatment which is best adapted to regulating the halogen content of the hydrocarbon conversion catalysts.

A preferred embodiment of the present invention is a method of regulating the halogen content of a hydrocarbon conversion catalyst prepared by impregnation of a support with at least one solution containing at least one element to be deposited on the support, said process comprising subjecting the catalyst to calcining, followed by washing with water and drying.

The extraction of the halogen by liquid water can be carried out by various means. If one operates at atmospheric pressure, it is necessary to select a contact temperature of between 30C and C, since below 20C.

the rate of extraction is verylow. If one operates at a pressure greater than atmospheric pressure, it is then possible to effect the extraction at a' temperature greater than 100C, which increases the rate of extraction of the halogen and therefore makes it possible to decrease the time of contact necessary for the extraction.

The duration of the extraction depends on the temperature at which it is carried out and also on the ratio of the volume of water to the volume of catalyst in contact. The extraction can be contained until the content of extracted halogen ions'in the extraction liquid no longer changes.

it is advantageous to use as wash water a water which does not contain the ions extracted; as wash agent one can use, for instance, condensed steam obtained after a distillation of the water coming from the washing of the catalyst.

The carrying out of the method of the invention leads to catalysts whose final halogen content in the catalyst is less than the initial content. Nevertheless it is not possible to extract the entire fixed amount of halogen.

The applicant has found and this result is entirely surprising that for the same halogen content, the catalyst of greatest stability is the one for which this content is obtained after an extraction treatment in accordance with the invention. A catalyst in connection with which this same halogen content has been obtained directly, that is to say without extraction, always exhibits poorer behavior with the passage of time. This result is entirely unexpected and is to be compared with the observations made by the applicant on catalysts prepared by conventional means, that is to say without dehalogenation phase.

This finding suggests the following explanation:

The halogenated compounds present on the catalyst are of various kinds; only those which are capable of being hydrolyzed, such as aluminum chloride, are extracted by washing. This explanation is confirmed by the results of-the, determinations set forth in Example ill which will be described below.

The process of the invention can be used on any hydrocarbon conversion catalyst, and in particular on hydroreforming catalysts. Thefollowing-examples which relate to hydroreforrning catalysts formed of platinum and another metal in free or combined form, which are deposited on alumina, do not constitute limitations on the invention either with'respect to the support or with respect to the hydrogenating-dehydrogenating compound, nor with respect to the third component which may perhaps not be present or may be replaced by another metal or various other metals.

EXAMPLE I PREPARATION OF THE CONTROL CATALYSTS 1 T1 and T2 Alumina is available in the form of extruded particles having the following characteristics:

Average diameter of the extruded particles 1.5 mm Specific surface 190 m /g Pore volume 0.5l em /g Average radius of the pores '53 A The first portion is immersed in 125 cc of a circulating solution containing:

11.25 cc 'of normal nitric acid, I

13.75 cc of normal hydrochloric acid 18.8 cc of hexachloroplatinic acid solution contain- I ing 9.31 g/l of platinum.

After 2 hours of circulation of the solution, its platinum is exhausted. The catalyst is centrifuged, dried. and then calcined at 400C for 3 hours. There is obtained a catalyst T1 the analysis of which, after a reductive treatment consisting in passing a stream of hydrogen over the catalyst for 2 hours at 500C, gives the following composition, expressed as elements, referred to the total weight of the catalyst:

platinum 0.3592 T1 tin 0.21% chlorine 0.9l'7z tion:

platinum 0.35% T2 tin 0.21% chlorine [14% PREPARATION OF CATALYST A A fraction of the catalyst T2, equal to 25 g, which has not undergone a reduction by hydrogen is introduced into a cartridge of a Soxhlet apparatus. The volume of distilled water serving as extraction agent for the elementary chlorine is equal to 200 cc. The extraction is effected for 24 hours, the average temperature of the water in contact with the catalyst being equal to about After drying, the catalyst obtained is reduced for 2 hours by a stream of hydrogen at 500C. There is obtained a catalyst A having the following composition:

platinum 0.35%

A tin 0.2 1 1 chlorine 0.92%

CATALYTIC TEST 25 cc of catalyst are placed in a stainless steel reactor. A stream of pure, dry hydrogen is passed over the catalyst for 2 hours, the temperature of the catalyst being maintained. at 500C and the pressure within the reactor being maintained at 7 bars. Thereupon, the temperature being increased to.5 10C, the charge consisting of n-heptane is introduced with a liquid hourly space volocity of 2and a ratio of the number of mols of hydrogen introduced to the number of mols of nheptanes introduced of 5.

Samples taken from the efflux of the reactor make it possible to determine on the one hand the liquid yield by simple weighing and on the other hand the equivalent octane number of the liquid by the application, to chromatographic analyses of the liquid, of the ASTM mixture numbers contained on nomograms.

TABLE I Catalyst Initial Octane points Average I Chlorine chlorine lost in 100 yield content content hours after test T1 0.91% 9.5 67.9 0.82 T2 1.14% 10.7 61.3 0.91 A 0.92% 5.7 64.8 0.86

Table I shows that catalyst A, obtained by the method of the invention is the most stable of the three catalysts tested. It is noted in particular that it is more stable than catalyst T1, whose chlorine content is practically the same.

EXAMPLE II PREPARATION OF THE CONTROL CATALYSTS T3 and T4 With an alumina identical to the one described in Example I there are deposited on it, after calcining for 4 hours at 600C, in succession tin and platinum under conditions identical to those described in Example I, except with regard to the amount of stannous chloride dihydrate contained in the firstimpregnation solution, which is equal to 0.27 g.

Two control catalysts are obtained having the-following compositions:

platinum 0.35%

T3 tin 0.15% chlorine 1.02%

platinum f 0.35%

T4 tin 0.15% chlorine 1.30%

PREPARATION OF CATALYST B platinum 0.35% B tin 0.15%

chlorine 0.95%

- CATALYTIC TEST The test carried out on the three catalysts T3, T4 and B under the conditions set forth in Example I leads to the results contained in Table II.

TABLE II Catalyst Initial Octane points Average Chlorine chlorine lost in yield content content hours after test T3 1.02 12.1 68.3 0.82 T4 1.30 26.0 67.8 1.00 B 0.95 10.3 70.9 0.84

It is noted that catalyst B of the invention is the most stable of the three catalysts, and that in particular, for a similar chlorine content, the catalyst B is more stable than catalyst T3.

EXAMPLE in A catalyst T is prepared by a method similar to that employed in Example I for obtaining catalyst T Catalyst T has the following composition after calcining in air at 400C:

platinum 0.35% T tin 0.20% chlorine 1.65%

25g of this catalyst are placed in the cartridge of a Soxhlet apparatus which contains 250 cc of distilled water. The treatment lasts for 24 hours. The extraction liquid is then concentrated to 100 cc. j

The determinations of chlorine (by gravimetry) and of aluminum (volumetry in the presence of ethylene diamine tetra-acetic acid EDTA) present in the extraction liquid give 1.84 g/l of chlorine and 0.46 g/l of aluminum respectively, which corresponds to a molar ratio of chlorine to aluminum of 3.04 (as compared with 300 for the theoretical value in Al C1 I 0.73% of the chlorine has been extracted (1.84 X 100/250) and 1.65 -0.73 =O.92% shouldtherefore remain on the catalyst; analysis gives 0.95%, which value is in good agreement andconfirms the dissolving of Al C1 by washing.

EXAMPLE IV PREPARATION OF CONTROL CATALYST T An alumina is used identical to that described in Example I. After it has been calcined at 6007C for 4 hours,

it is immersed in ahydrochloric acid solution of chloroplatinic and perrhenic acids. The mixture is placed in a rotary evaporator. The product obtained is dried at C, and then calcined in air at 530C for 2 hours. The product obtained is divided into two portions.

One portion of the product obtained is subjected to a reductive treatment consisting in passing hydrogen over it'for 2 hours at500C.

Catalyst T is obtained, the composition of which by weight is as follows:

platinum 0.33% T rhenium 0.20%

chlorine PREPARATION OF CATALYST C The second portion is subjected to extraction by liquid water in a Soxhlet apparatus in accordance with the method described in Example I.

The catalyst C'obtained after drying and reduction at a temperature of 500C by a stream of hydrogen for 2 hours has the following composition:

platinum 0.33%

C rhenium 0.20%

chlorine 0.85%

CATALYTIC TEST The test on the catalysts were carried out under conditions similar to those described in Example I. These tests were carried out for two pairs of values of the pressure and liquid hourly volumetric velocity (v.v.h.

namely 7 bars 2 vvh, and 14 bars l vvh respectively, all other things-being equal.

The results are set forth in Table III which appears at the end of Example V.

EXAMPLE v 4 PREPARATION or THE CONTROL CATALYST T An alumina is used identical tothat described in Ex- I ample I. After it has been calcined at 600C for 4 hours, it is immersed in a germanium chloride (Ge Cl solution in absolute alcohol acidified by HCl. This solution is evaporated in a rotary evaporator, dried at 120C and then calcined at 600C for 2 hours. I

The product obtained is then subjected to circulation of l N HCl for 24 hours and then dried. The resultant product is subjected to the circulation of a'hydrochloric acid solution of hexachloroplatinic, acid until the platinum contained in the solution has been exhausted. The catalyst is dried and calcined for 3 hours at 530C. The product obtained is divided into two portions.

The first portion is subjected to a reductive treatment by passage of hydrogen .at 500C for 2 hours. There is obtained a catalyst T having the following compositron:

platinum T; germanium 0.14% chlorine 1.36%

platinum 0.37 Z

I D I germanium 014% chlorine 0.88%

CATALYTIC TEsT TABLE III Catalnitial Octane Average Chlorine lysts chlorine points yield content content lost in after 7 (72) hrs test (72) T l.l8 I3 703 0,37 7 bars C 0.85 7.9 75.7 0.54

2 vvh T, 1.36 2.8 64.4 1.05 D 0,88 2,8 68A 0.85 T M8 2.5 44.3 0.84 C 0.85 1.. 52.6 0.49

l4 burs T, L36 )9 47 L20 1- vvh D 0.88 0,9 5 L4 0.86

EXAMPLE VI PREPARATION OF THE CATALYSTS T8, T and E 'Three catalysts T T and E are prepared under conditions similar to those described in Example Ifor the catalysts T T and A respectively. The catalysts obtained have the following compositions:

platinum 0.36%

T tin 0.2 l '7: chlorine 0.92%

platinum 0.37%

T,, tin 0.20% chlorine 1.33 7! platinum 0.37%

E tin 0.20% chlorine 0.8971

CATALYTIC TEST The three catalysts thus prepared are then tested in identical parallel tests carried out on 100 cc of catalyst under the following operatingconditions:

vvh of the liquid charge 14 total pressure in the reactor [5.5 bars ratio of the number of mols I introduced. hydrogen/charge 6 The hydrocarbon charge has the following properties:

ASTM initial boiling point 68C temperature at which 50% of the volume is distilled C ASTM final boiling point 144C density measured at 20C 0.7 l5 Components by volume:

paraffin hydrocarbons 68% naphthenes 25% aromatics 7% After reduction of the catalyst in a stream of pure hydrogen at a temperature of 510C, the temperature is lowered to 370C, at which temperature the hydrocar bon charge is introduced gradually, while the temperature is increased, also gradually, until the operating conditions mentioned above are satisfied for a research octane number of the liquid fraction (without addition of tetraethyl lead) of 98. For the entire duration of the test, this severity is retained by increasing the temperature if necessary.

In Table IV there have been set forth for values in hours of the time of the tests (withoutinterruption) the values of the yield in hydrocarbons having live or more the weight of the catalyst, where the percentage of chlorine is calculated on the-basis of the elemental form.

6. In a process for the preparation of a hydrocarbon during theimpregnation step; thereafter calcinated and then washed with liquid water to remove substantially all the waterextractable chlorides to leave a more stabilized final chlorine content of between 0.5 and 1.2% of C g introduced (measured in l q d State at 5 conversion catalyst which consists essentially of a chloand expressed in liters). rinated porous support of a refractory oxide and plati- TABLE IV Catalysts T9 E TM Number of hours of operation 306 618 332 64] 330 642 Yield c,+ as 64 71.6 69,4 17.4 66,2

Yield H, (U!) 142 123 153 141 148 I36 This table shows the advantages of catalyst E over the num and consisting essentially of impregnating said catalysts T (of a composition substantially equivalent support with a solution containing at least one element to that of E but not Subjected to an extraction) and 9- to be deposited on the support and then calcinating the We claim: impregnated support; the improvement for stabilizing 1. A chlorinestabilized hydrocarbon conversion catthe chloride content of the catalyst consisting essenalyst consisting essentially of a chlorinated support, tially of over-chlorinating said catalyst originally; washsaid support being a porous refractory oxide, and platiing said catalyst with water in liquid form subsequent num deposited on said support by impregnat With a to said calcinating to extract chlorides, then drying said solution containing platinum,said catalyst having been catalyst,

over-chlorinated during the impregnation step, thereaf: 7. I a m thod according to claim 6, wherein the ter calcinated and then washed with liquid water to reashing is arried out above 100C at a .pressure move substantially all the water-extractable chlorides greater h t h i pressure to leave a more stabilized final chlorine content of beg [n a h d according to l i h i h p tween 0.5 and 1.2% of the weight of the catalyst, where alyst i fixgd hil th water ir l t the percentage of chlorine is calculated on the basis of 9 I a h d according to l i 6, h i th the elemental formwater is purified by distillation before it is contacted 2. A catalyst as claimed in claim 1, wherein said final h the Catalyst 3 Content is between and (19%- v 10. In a method according to claim 6, wherein the A Chlorine-Stabilized hydrocarbon conversion chlorine content of said catalyst is between 05 andalyst consisting essentially of a chlorinated support;

Said pp being a Porous refractory Oxide; Platinum 11. In a method according to claim 6, wherein the imand an additional p Chosen f the grfmp provement further comprises sufficiently overconslting of g m andfhemum 'deposlied 4O chlorinating such thatthe subsequent washing removes i support by 'mpregnanon with at least a solution substantially all of the accessibly hydrolyzable chloride Containing i least one element to be deposlted 9 the compounds from said catalyst so as to reduce the chlo- Support; t havmg been over'cblormated rine content thereof to between 0.5 and 1.2% of the during the i f q Step; thereafter Calcmated.and weight of the catalyst, when the percentage is calcuthen washed w1th l1qu1d water to remove substantially lated as if in elemental form;

allthe water-extractable chlorides to leave a more sta- 12. In a method according to claim 11, wherein the bihzed final chlorme content of between 0.5 and 1.2% Support contains alumina and the platinum is deposited of weight of the Catalyst wher? petccmage of from a chloroplatinic acid solution.

gilllgqrme 1s calculated on the basls of the elemental In a method according to claim 11 wherein the 4. catalyst as claimed in claim 3, wherein said final n 3 252: $2353; 222%; 23:21a (W chlorme cmltent Pi and ment wherein said catalyst additionally contains tin.

5. A chlorme-stabihzed hydrocarbon convers1on catalyst consisting essentially of a chlorinated support;. In a m accordmg 9 13, p Said Support being a porous refractory Oxide; platinum rnent wherein said catalyst add1t1onally contams germaand two additional compounds chosen from the group consisting of tin, germanium and rhenium, deposited In a method accotdmg to Claim 13, the "t pt on said support by impregnation with at least a solution ment wherein Said catalyst additionally comams containing at least one element to be deposited on the ntumsupport; said catalyst having been over-chlorinated -1" a method a r g to Claim wherein the said catalyst additionally contains two additional metals chosen from the group consisting of tin, germanium,

and rhenium.

V UNITED STATES PATENT OFFICE. CERTIFICATE OF CORRECTION Patent i 2, Dated December 3, .1974

lnventofls) Philippe Enqelhard and Joseph Edouard Weisang I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, Claim 2, line 5A after "final" insert -chlorine-.

Signed and sealed this llth day of F b 1975,

(SEAL) Attes't: U

C. MARSHALL DANN RUTH t MASONJ Commissioner of Patents Attes-tlng Off cer and Trademarks FORM Po-1050 (10-69) uscomM-DC 5037s was 9 U. S. GOVERNMgNT PRINTING OFFICE: I96! 0-366-334 

1. A CHLORINE-STABILIZED HYDROCARBON CONVERSION CATALYST CONSISTING ESSENTIALLY OG A CHLORINATED SUPPORT, SAID SUPPORT BEING A POROUS REFRACTORY OXIDE, AND PLATINUM DEPOSITED ON SAID SUPPORT BY IMPREGNTION WITH A SOLUTION CONTAINING PLATINUM, SAID CATALYST HAVING BEEN OVER-CHLORINATED DURING THE IMPREGNATION STEP, THEREAFTER CALCINATED DURING THE LIQUID TO REMOVE SUBSTANTIALLY ALL THE WATER-EXTRACTABLE CHLORIDE TO LEAVE A MORE STABILIZED FINAL CHLORINE CONTENT OF BETWEEN 0.5 AND 1.2% OF THE WEIGHT OF THE CATALYST, WHERE THE PERCENTAGE OF CHLORINE OR CALCULATED ON THE BASIS OF THE ELEMENTAL FORM.
 2. A catalyst as claimed in claim 1, wherein said final content is between 0.5 and 0.9%.
 3. A chlorine-stabilized hydrocarbon conversion catalyst consisting essentially of a chlorinated support; said support being a porous refractory oxide; platinum, and an additional component chosen from the group consisting of tin, germanium and rhenium, deposited on said support by impregnation with at least a solution containing at least one element to be deposited on the support; said catalyst having been over-chlorinated during the impregnation step; thereafter calcinated and then washed with liquid water to remove substantially all the water-extractable chlorides to leave a more stabilized final chlorine content of between 0.5 and 1.2% of the weight of the catalyst, where the percentage of chlorine is calculated on the basis of the elemental form.
 4. A catalyst as claimed in claim 3, wherein said final chlorine content is between 0.5 and 0.9%.
 5. A chlorine-stabilized hydrocarbon conversion catalyst consisting essentially of a chlorinated support; said support being a porous refractory oxide; platinum, and two additional compounds chosen from the group consisting of tin, germanium and rhenium, deposited on said support by impregnation with at least a solution containing at least one element to be deposited on the support; said catalyst having been over-chlorinated during the impregnation step; thereafter calcinated and then washed with liquid water to remove substantially all the waterextractable chlorides to leave a more stabilized final chlorine content of between 0.5 and 1.2% of the weight of the catalyst, where the percentage of chlorine is calculated on the basis of the elemental form.
 6. In a process for the preparation of a hydrocarbon conversion catalyst which consists essentially of a chlorinated porous support of a refractory oxide and platinum and consisting essentially of impregnating said support with a solution containing at least one element to be deposited on the support and then calcinating the impregnated support; the improvement for stabiliZing the chloride content of the catalyst consisting essentially of over-chlorinating said catalyst originally, washing said catalyst with water in liquid form subsequent to said calcinating to extract chlorides, then drying said catalyst.
 7. In a method according to claim 6, wherein the washing is carried out above 100*C at a pressure greater than atmospheric pressure.
 8. In a method according to claim 6, wherein the catalyst is fixed, while the water circulates.
 9. In a method according to claim 6, wherein the water is purified by distillation before it is contacted with the catalyst.
 10. In a method according to claim 6, wherein the chlorine content of said catalyst is between 0.5 and 0.9%.
 11. In a method according to claim 6, wherein the improvement further comprises sufficiently over-chlorinating such that the subsequent washing removes substantially all of the accessibly hydrolyzable chloride compounds from said catalyst so as to reduce the chlorine content thereof to between 0.5 and 1.2% of the weight of the catalyst, when the percentage is calculated as if in elemental form.
 12. In a method according to claim 11, wherein the support contains alumina and the platinum is deposited from a chloroplatinic acid solution.
 13. In a method according to claim 11 wherein the catalyst comprises a support which is alumina.
 14. In a method according to claim 13, the improvement wherein said catalyst additionally contains tin.
 15. In a method according to claim 13, the improvement wherein said catalyst additionally contains germanium.
 16. In a method according to claim 13, the improvement wherein said catalyst additionally contains rhenium.
 17. In a method according to claim 13, wherein the said catalyst additionally contains two additional metals chosen from the group consisting of tin, germanium, and rhenium. 